Tongs have long been used in oilfield operations to grip and rotate lengths of tubular members, thus "making up" or "breaking apart" joints of pipe. The tong performing the rotating operation or an upper pipe is generally referred to as the power tong, and the tong used to grip and prevent rotation of the lower pipe joint is generally referred to as a back-up tong. Back-up tongs may be either powered or manually operated, and their use is optional depending, in part, on the likelihood that the lower pipe would otherwise rotate in response to make up torque being transmitted to the upper pipe by the power tong.
Power tongs may be generally classified as either open throat or closed throat. Closed throat tongs generally have a circular ring member which fully encompasses the joint of pipe during the make up operation. An advantage of the closed throat or donut-type power tong is that the tong body and rotatable gear will not easily spread, and the tong is therefore capable of transmitting high torques to the pipe joint. Such tongs have a disadvantage, however, in that the tong cannot easily be laterally put on or taken off the string or pipe. In another version of a closed throat tong, a section of the gear is pivotable, so that lateral movement of the tong with respect to the drill string is possible. Such tongs are generally of the closed throat type, however, since the gear completely encompasses the joint of pipe during the make up operation. Examples of closed throat tongs are disclosed in U.S. Pat. Nos. 3,371,562, 3,483,774, 3,507,174, 3,550,485, 3,589,742, 3,635,105, and 4,334,444.
Many tong operators prefer an open throat tong, which is characterized by an open throat tong body portion with an optional latch door. Such tongs generally utilize a partial ring member having an open throat portion, so that the door may be opened and the throat of the tong body aligned with the throat of the partial ring. Open throat tongs thus have an operational advantage compared to closed throat tongs because the tongs may easily be laterally moved on and off a string of pipe. A disadvantage of the open throat design, however, is that such tongs may experience problems associated with "spreading" of the open throat portion, especially during high torque operations. Examples of open throat tongs are shown in U.S. Pat. Nos. 2,989,880, 3,021,739, 3,180,186, 3,196,717, 4,084,453, 4,170,907, and 4,346,629.
Most open throat tong bodies include a generally U-shaped front portion including the open throat adapted to receive the tubular member, and a rearward motor and gear train portion including a tail piece adapted for either a snub line or a back-up tong engaging bar. A snub line may be used to "tie off" the tong to prevent tong rotation while the joint of pipe is being made up. The engaging bar prevents axial rotation of the power tong by fixing the power tong body relative to the back-up tong, which is fixed to the lower string of pipe. Most power tongs are adapted for front entry, that is, the open throat portion of the tong is along the curvilinear portion of the U-shaped front portion and opposite the pair of drive gears with respect to the ring member centerline, as shown in U.S. Pat. No. 4,084,453.
A side-entry scissors-type tong is shown in U.K. Pat. No. 656,738. This tong includes a spinner, an upper tong body, and a lower tong body. The tong bodies rotate in scissors fashion relative to one another for accomplishing the final make up or the initial break out of the joint. A "angled entry" tong is shown in U.S. Pat. Nos. 2,846,909 and 2,950,639. These latter tongs are of the closed throat type since the gear completely encompasses the tubular member. The gear halves may be latched and unlatched by sets of vertically movable keys, and the gear halves may thus be opened to allow the tong to move on or off the pipe. An "angled-entry" open throat casing tong has also been manufactured and sold by Hillman-Kelley.
Each power tong is generally directed to a range of pipe diameters. Casing tongs handle casing in the range of 51/2 inches to 24 inches O.D.; drill pipe tongs are generally designed for 51/2 inchs to 111/4 inch O.D. pipe; tubing tongs frequently handle 23/8 inches to 75/8 inches O.D. tubing. Macaroni tubing (31/2 inch O.D. and under) is typically used in recovery and hydraulic workover operations. In many operations, two or more strings of tubing are made up for placement within a casing, so that the strings of tubing are necessarily close together.
Most tongs are not particularly adapted for small diameter tubing. U.S. Pat. No. 4,246,809 discloses a power tong specifically designed for macaroni tubing, but this tong is of the closed throat type. Accordingly, the tong body cannot be laterally put on or taken off the pipe. The tubing must therefore pass through the tong as successive joints are made up, which may damage the tubing and/or the tong. Also, if a problem develops with the tong operation, the tong cannot be easily removed from the string of pipe.
Another tong capable of making up and breaking apart tubing is shown in U.S. Pat. Nos. 3,380,323 and 3,380,324, (hereinafter referred to as the Hillman-Kelley tubing tong), with an optional back-up tong shown in U.S. Pat. No. 3,387,512. The Hillman-Kelley tubing tong, however, experiences a number of problems in field operations because of its limited torque output and the frequency of repair due, in part, to the large number of moving components. Higher make up and break out torque capabilities for tubing tongs enable more varied use of the tongs and thus more efficient drilling operations. Tong operators also universally recognize that the cost associated with repair or replacement of a tong is nominal compared to the cost associated with stoppage of the drilling operation due to a tong breakdown.
A further problem associated with the Hillman-Kelley tong lies in its inability to be easily utilized to make up dual tubing strings, although the tong is widely utilized in dual string tubing operations. As previously stated, two or more tubing strings may be made up within a casing for production operations, so that a first tubing string is separated from a like tubing string by inches (generally the tubing centerlines are at 6 inch spacings). The design of the Hillman-Kelley tong is generally compact, so that one tubing string can be made up within the tong while a second tubing string is in engagement with the outer body of the tong. In many operations, however, the strings of tubing are so close together that the Hillman-Kelley tong can only be employed if the spacing between the two strings of pipe is increased. The Hillman-Kelley tong may be moved higher off the drilling rig floor, thereby allowing the flexing of the tubing strings to widen the spacing between the strings and thereby enable tong operation.
Although the above procedure has been widely utilized for years, it has a number of significant disadvantages. Additional operator time is required to spread the tubing apart above the rig floor, and this operation can bend tubing thereby making subsequent tubing handling more difficult. Also, the rig is not generally designed to have the tong positioned above the rig floor, so that make-shift operator platforms may be utilized or the tong operated without the operator being able to properly view the make up operation. Thus, an unsafe working environment may be created, and the tong may not be reliably utilized to efficiently make up or break apart dual strings of tubing.
The disadvantages of the prior art are overcome by the present invention, and an improved power tong is hereafter disclosed for making up and breaking apart joints of tubing. An improved method is also disclosed for making up dual string joints of tubing utilizing the power tong of the present invention.